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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var a = 10;
        ++a; //11
        var b = ++a + 2; //12+2
        console.log(b); //14

        var c = 10;
        c++;
        var d = c++ + 2;
        console.log(d); //13

        var e = 10;
        var f = e++ + ++e; //10+12
        console.log(f); //22
        //后置自增 先表达式返回原值 后面变量再自加1
    </script>
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